Of course, in such a case you will check ulimits -u / limits.conf (nproc) and sysctl.conf (kernel.pid_max). But what if this does not help?

SUSE introduced a new Thread Limit using the PID cgroup controller. Its default value is 512, and obviously too small for any production RAC I ever saw. If your ohasd cgroup violates it, you will get one tiny and singular error message in dmesg and many of the above, uncertain ORA-27300 “fork failed with status:11”. And did you know what “11” is? it means “Try again”. :) Thank you.